I just went 18 with a Schick Proline; last year went 22 with a KAI Mild. Normally, I use a blade for 2 weeks (up to 12 shaves) then change - quite sure I could do this with Feather Pro or Pro Super as well. Never tried the guarded blades.
I get about 7 in an SE razor, but in the Feather SS I went to about 14 or 15 (although I wasn't using the SS for the entire shave, so I guess it's not a good comparison). The blade I use is the Schick Proline.